Electroluminescent voltage measuring device



Original Filed June 26, 1958 INV ENT OR Lieb ATTORNEY United StatesPatent 3,149,281 ELECTROLUMINESCENT VOLTAGE MEASURlNG DEVICE AlbertLieh, Stuttgart-Bad Cannstatt, Germany, assignor to InternationalStandard Electric Corporation, New York, N.Y., a corporation of DelawareOriginal application June 26, 1958, Ser. No. 744,846. Divided and thisapplication Mar. 1, 1961, Ser. No. 92,631

Claims priority, application Germany July 5, 1957 3 Ciaims. (Cl. 324-96)This invention relates to a device for indicating the magnitude of anelectric voltage by means of an electroluminescent panel.

This is a divisional application of my copending application Serial No.744,846, filed June 26, 1958, and now abandoned.

Devices are known in which an electroluminescent substance is exposed toan electric field across a capacitor and is thus stimulated for theemission of light. In such arrangements the intensity of the lightemission depends upon the magnitude of the electric field intensity, orthe applied Voltage. For this reason simple types of luminescentcapacitors have already been used for the voltage indication, whereinthe brightness of the excited luminescing layer served as a measure ofthe magnitude of the voltage. Such an indication, however, is veryinaccurate, because the human eye is insensitive to smaller variationsof the light emission.

For this reason it is one object of the present invention to achieve aclearly visible voltage indication with the aid of electroluminescentcapacitors by variation of the luminous pattern in size. This isaccomplished by a device for indicating the magnitude of an electricvoltage, in which between two electrically conductive layers, of whichat least the one is optically transparent, there is arranged anelectro-luminescence substance. At least one of these coatings has anelectrical resistance of such a high value that upon application of avoltage at the one end of this resistance a light emission will at.first only substantially appear at this point and which, withincreasing voltage, will continuously extend to further surface areas ofthe luminescent capacitor.

According to the invention a sharp boundary between the luminous and thenonluminous indicating area may be achieved by positioning between thetwo conductive coatings, an additional voltage-dependent layer whoseresistance is changed or varied abruptly at a predetermined voltagelevel. It is particularly advantageous to employ a material, such ascadmium sulphide, which has the property of providing avoltage-dependent resistance layer.

In the following the invention will now be described in particular withreference to the accompanying drawings in which:

FIG. 1 diagrammatically illustrates an indicating surface or area inwhich the indicating condition is illustrated by crosshatch lines;

FIG. 2 is a sectional view of an electroluminescence capacitor accordingto FIG. 1; and

FIG. 3 is an example similar to FIG. 2 illustrating an embodiment of theinvention.

To a suitable carrier or base 1, e.g. an optically transparent base ofglass or mica there is applied a conductive layer 2 which may likewisebe of the optically transparent type. Such a layer may be produced byevaporation of metals, such as aluminum, in a vacuum, or by causingvapors of metal salts, such as SnCl SnCL, or TiCl to react with theheated base. In the latter case there will be formed anelectrically-conductive coating of metallic oxide. When employing SnO orTiO this ice coating will be transparent. On the electrically-conductivelayer 2 there is arranged a layer of a suitably preparedelectro-luminescent phosphor substance 4, such as zinc sulphide with acopper activator added in excess. The luminous substance isadvantageously embedded in a dielectric having a high dielectricconstant, e.g. in polyacrylic acid-ester.

The electroluminescent layer is followed by a resistance layer 3. Thismay be a thin layer of metal consisting e.g. of aluminum which isevaporated in the vacuum, or else of a layer of graphite which isapplied by spraying. The lead-in conductors for the voltage exciting orelectrically stimulating the luminous substance, such as by alternatingvoltage, are applied to the conductive layer 2 and to the resistancelayer 3.

The value of the resistance is so chosen that upon application of theexciting voltage to the electrodes 2 and 3 there will appear anoticeable voltage drop along the resistance. In this Way it is possibleto achieve the resuit that the luminous area will be continuously andsteadily enlarged in direction towards the gradient of the voltage dropupon application of the exciting voltage.

An example of an embodiment of the invention is shown in FIG. 3. In thiscase there is provided between the resistance layer 3 and theelectroluminescent layer 4 a further layer 8, the electrical resistanceof which is abruptly reduced upon increase of the applied voltage to apredetermined threshold value. Such a layer may e.g. consist of a knownsuitably prepared CdS or of silicon carbide. This arrangement has theadvantage that the boundaries of the luminous pattern are particularlysharply distinguished. This will be apparent as the electroluminescentlayer 4 will glow more brilliantly in the region extending fromterminals 5 to the point on layer 4 at which the critical voltage isreached. By this the reading is substantially facilitated and thesensitivity is substantially increased. In this figure instead ofdepending only on the capacitive shunting between the conductive layersto provide the limit of the voltage drop there is provided a resistor 7connected between one of the leads to voltage source 5. The other end ofthe resistor is connected with the far end of the resistance layer 3.Thus, there will be produced a voltage drop along resistance layer 3dependent upon the value of resistor 7. The potential difference betweenresistance layer 3 and the coating 2 will diifer from that at theterminal 5 by the voltage drop in the resistor 7.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

What is claimed is:

l. A device for indicating the magnitude of an electric voltage by thevariation in extent of a luminous pattern, comprising two electricallyconducting coatings, of which at least one is optically transparent, oneof said conducting coatings having an electrical resistance relativelyhigher than the other, a continuous voltage-dependent resistance layerthe resistance of which changes abruptly at a predetermined voltagelevel to give a sharp boundary between the luminous and non-luminouspattern, a layer of electroluminescent substance continuously adjoiningsaid voltage-dependent resistance layer, said electroluminescentsubstance and said resistance layer positioned between said coatings andhaving uniform thicknesses therealong, and means for applying a voltagebetween one end of said resistance coating and the other coating,whereby upon application of a predetermined voltage a light emissionwill at first only appear substantially at the point of ap- 2 plication,but will continuously extend to further surface areas of the luminouspattern as the voltage is increased.

2. A device as claimed in claim 1, wherein said voltage-dependentresistance layer consists of cadmium sulphide.

3. A device according to claim 1, including a fixed resistive deviceconnected between the other end of said higher resistance coating andsaid means for applying said voltage.

References Cited in the file of this patent UNITED STATES PATENTS DiemerJuly 17, 1956 Peek Dec. 31, 1957 Kazan Sept. 9, 1958 Mash Mar. 15, 1960

1. A DEVICE FOR INDICATING THE MAGNITUDE OF AN ELECTRIC VOLTAGE BY THEVARIATION IN EXTENT OF A LUMINOUS PATTERN, COMPRISING TWO ELECTRICALLYCONDUCTING COATINGS, OF WHICH AT LEAST ONE IS OPTICALLY TRANSPARENT, ONEOF SAID CONDUCTING COATINGS HAVING AN ELECTRICAL RESISTANCE RELATIVELYHIGHER THAN THE OTHER, A CONTINUOUS VOLTAGE-DEPENDENT RESISTANCE LAYERTHE RESISTANCE OF WHICH CHANGES ABRUPTLY AT A PREDETERMINED VOLTAGELEVEL TO GIVE A SHARP BOUNDARY BETWEEN THE LUMINOUS AND NON-LUMINOUSPATTERN, A LAYER OF ELECTROLUMINESCENT SUBSTANCE CONTINUOUSLY ADJOININGSAID VOLTAGE-DEPENDENT RESISTANCE LAYER, SAID ELECTROLUMINESCENTSUBSTANCE AND SAID RESISTANCE LAYER POSITIONED BETWEEN SAID COATINGS ANDHAVING UNIFORM THICKNESSES THEREALONG, AND MEANS FOR APPLYING A VOLTAGEBETWEEN ONE END OF SAID RESISTANCE COATING AND THE OTHER COATING,WHEREBY UPON APPLICATION OF A PREDETERMINED VOLTAGE A LIGHT EMISSIONWILL AT FIRST ONLY APPEAR SUBSTANTIALLY AT THE POINT OF APPLICATION, BUTWILL CONTINUOUSLY EXTEND TO FURTHER SURFACE AREAS OF THE LUMINOUSPATTERM AS THE VOLTAGE IS INCREASED.